How Niagara Falls Was Formed: Geology & Fun Facts
12,000 years of geology in plain English. How a glacier created the falls, why they move upstream, and the facts that make the science interesting.
In This Guide
The Glacier That Started Everything
About 12,000 years ago, the Laurentide Ice Sheet — a glacier that covered most of Canada — retreated northward. As it melted, it uncovered the Great Lakes basin. Lake Erie's meltwater found a path toward Lake Ontario, carving through layers of rock that had been deposited over 450 million years.
That water path became the Niagara River. The falls began where the river dropped off a hard layer of dolostone onto softer shale below. That location was not where the falls are today — it was 11km downstream, at what is now Queenston-Lewiston.
Why the Falls Move Upstream
The key to understanding Niagara Falls is that the top rock layer (dolostone) is harder than the rock beneath it (shale). The water erodes the soft shale, creating an overhang of hard dolostone. Eventually, the unsupported dolostone collapses.
This cycle repeats endlessly — erode the soft rock, collapse the hard cap, retreat upstream. The falls have moved 11km in 12,000 years, retreating at roughly 30cm per year historically.
Since the 1950s, water diversion for hydroelectric power has slowed erosion significantly. Left unchecked, the falls would retreat to Lake Erie in about 50,000 years.
The Numbers
Horseshoe Falls height: 51 metres (167 feet) Horseshoe Falls width: 670 metres (2,200 feet) American Falls height: 21-34 metres (70-110 feet) Water flow: 750,000 US gallons per second (natural), ~375,000 (with diversion) Age: approximately 12,000 years Retreat rate: ~30cm/year historically, much slower now Rock layers: 450-million-year-old dolostone over shale
Is Niagara Falls Man-Made?
No. Niagara Falls is entirely natural — formed by glacial retreat and river erosion over 12,000 years. However, the amount of water flowing over the falls IS controlled by humans.
Since the 1950 Niagara Diversion Treaty between Canada and the US, about half the river's water is diverted through underground tunnels to hydroelectric generating stations before it reaches the falls. At night and during winter (when fewer tourists are watching), even more water is diverted.
The falls would look roughly twice as powerful without the diversion. But the power generated supplies about 25% of Ontario's and New York State's electricity.
The Day the Falls Stopped
On March 29, 1848, an ice dam formed at the mouth of Lake Erie, blocking the Niagara River upstream. The falls went virtually dry for about 30 hours.
Locals walked on the exposed riverbed. Artifacts and weapons from centuries past were found. Two mills that relied on river power went silent for the first time in decades. When the ice dam broke, the water returned with a roar heard for kilometres.
This has not happened since. Modern ice control measures prevent the conditions that caused it.
Frequently Asked Questions
Is Niagara Falls man made?
No. The falls are natural, formed 12,000 years ago by glacial meltwater. However, the water flow IS controlled — about half is diverted for hydroelectric power.
How old is Niagara Falls?
Approximately 12,000 years, formed when the last ice age glacier retreated and exposed the Great Lakes basin.
Are Niagara Falls getting smaller?
The falls retreat upstream about 30cm per year as water erodes the underlying shale. Water diversion for hydroelectric power has significantly slowed this process since the 1950s.
Did Niagara Falls ever stop flowing?
Once — on March 29, 1848, an ice dam blocked the river for about 30 hours. People walked on the dry riverbed. It has not happened since.